The Daimler Chrysler Corporation has produced a number of automatic transmissions, three of which are model numbers 46RE, 47RE and 48RE. Each of the 46RE, 47RE, and 48RE transmissions have four gears (the fourth gear also referred to as overdrive) and are fully automatic transmissions with electronic governors and lock-up-clutch-equipped torque converters. FIG. 13 is a hydraulic circuit diagram of a portion of the 46RE and 47RE hydraulic shift control system 1300. Control system 1300 includes a manual valve 1302 that receives a user input for shifting the transmission into one of the four forward gears, reverse, or park, a pressure regulator valve (PRV) 1304 for controlling main line pressure, a boost valve 1306 for causing the PRV to increase main line pressure under certain conditions, and a lock-up switch valve 1308 for engaging the torque converter lock-up clutch (TCC). Pressurized transmission fluid originating from pump output 1310 is distributed to a series of fluid passageways in the control system 1300, including being distributed to PRV 1304 at cutback ports 1312, 1314, 1316, and 1318, and line pressure port 1319. Prior to entering cutback ports 1312, 1314, 1316, and 1318 the transmission fluid passes through flow restricting orifices 1320, 1322, 1324, and 1326 located in a valve body separator plate (FIG. 5). Pressurized transmission fluid from throttle valve output 1330 acts on PRV 1304 at throttle valve port 1332. PRV 1304 also includes a spring 1333 that, from the vantage point of FIG. 13, urges the PRV to the left.
Boost valve 1306 is in fluid communication with a transmission fluid exhaust reservoir 1334 (denoted by an “X”) which is a low-pressure location in hydraulic shift control system 1300. Control system 1300 also includes an exhaust passage 1340 providing fluid communication between cutback port 1318 and boost valve 1306. Boost valve 1306 is disposed in a boost valve bore (not illustrated) in a valve body casting 202 (FIG. 2) and is movable between a first position, where exhaust passage 1340 is not in fluid communication with exhaust reservoir 1334 and a second position (as illustrated in FIG. 13), where the exhaust passage is in fluid communication with the reservoir, thereby causing the fluid pressure at cutback port 1318 to decrease.
During use, the 46RE and 47RE PRV 1304 controls transmission main line pressure via the position of the PRV within the PRV bore (not illustrated). Line pressure increases as PRV 1304 moves to the left, away from spring 1333, and towards an increased line pressure position, and decreases as the PRV moves to the right, towards a reduced line pressure position. Fluid pressure at cutback ports 1312, 1314, 1316, and 1318 urge PRV 1304 to the right, thereby tending to urge the PRV towards a reduced line pressure position and decrease line pressure, and fluid pressure at throttle valve port 1332 and the force of spring 1333 urge PRV 1304 to the left, thereby tending to increase line pressure. The position of PRV 1304 at any given time is a function of the balancing of these forces.
The 46RE and 47RE transmissions are configured to increase main line pressure when the transmission is in fourth gear and when the TCC is engaged. One benefit of increasing line pressure in fourth gear is that higher line pressure increases fluid flow through the transmission cooler, thereby increasing heat removal from the transmission. One benefit of increasing line pressure when the TCC is engaged is to increase the TCC lock-up clutch apply force to help ensure adequate TCC lock-up. Line pressure is increased for both fourth gear and TCC lock-up by exhausting cutback port 1318 to exhaust 1334 via exhaust passage 1340. This is accomplished by causing boost valve 1306 to open, thereby placing exhaust passage 1340 in fluid communication with exhaust 1334. Although cutback port 1312 is in fluid communication with cutback port 1318, the combination of pressurized fluid from pump output 1310 and flow restricting orifice 1320 maintain fluid pressure at cutback port 1312 even when boost valve 1306 is open, such that pressure is only reduced at cutback port 1318 and not at cutback port 1312 when the boost valve opens.
As with the 46RE and 47RE transmissions, the 48RE transmission also increases line pressure in fourth gear and when the TCC is engaged, however, the 48RE includes an alternative design that results in a larger line pressure increase that results in improved transmission cooling in fourth gear due to increased flow through the transmission cooler and improved TCC clutch engagement, which reduces the likelihood of TCC wear from insufficient clamping force. These modifications make the 48RE more desirable, however, 48RE valve bodies are in short supply and more expensive than the 46RE and 47RE transmissions and valve bodies.